1. Field of the Invention
The present invention relates to a small magnetic disk cartridge that can be exchangeably loaded in a card disk drive that can be loaded in the card slot of electronic equipment such as a digital still camera, a digital video camera, a laptop personal computer, etc.
2. Description of the Related Art
To record or reproduce information, a wide variety of recording media are removably loaded in the card slot of electronic equipment such as a digital still camera, a digital video camera, a laptop personal computer (PC), etc. Such recording media that are in practical use are a semiconductor memory type, a hard disk type, an optical disk type, a magnetic disk type (e.g., a floppy disk type), etc.
Among these recording media, the semiconductor memory type is most widely used, because it is easy to handle and has a large recording capacity. However, the semiconductor memory type is relatively expensive. Therefore, in digital cameras employing the semiconductor memory type, it is repeatedly used by storing the photographed image data in a PC, etc., and then deleting the data from the semiconductor memory.
Although there are known some hard disks that can store 340 megabytes (MB) of data or 1 gigabytes (GB) of data. However, the hard disk type memory medium is similarly expensive. Because of this, the hard disk type memory medium is repeatedly used by storing data in a PC, etc.
The optical disk type has a large recording capacity for its size. For example, an optical disk with a size of 35 mm×41 mm×11 mm can store 256 MB of data. Optical disks with a recording capacity of 512 MB are about to be realized. However, optical disks have the disadvantage that the recording speed is slow, because the writing time is time-consuming.
Small magnetic disks (e.g., floppy disks) with a size of about 50 mm×55 mm×2 mm are known that can be exchangeably loaded in a disk drive of a size that can be inserted in the card slot of a PC, etc. However, the recording capacity is as small as 40 MB and insufficient to store data photographed by a camera. In addition, the size is not suitable for digital cameras.
With the spread of PCs, digital cameras have spread rapidly in recent years because of the easy method of recording, enhancement of the picture quality due to the development of imaging devices, the possibility of data deletion and transmission, size of the recording capacity, etc. However, digital cameras are restricted in use, because recording media are restricted in cost and recording capacity, as described above. For instance, since recording media are very expensive, one camera is usually provided with one recording medium, which is repeatedly used. That is, when the recording medium is filled with data, the data is transferred to a PC and deleted from the recording medium. Because of this, there are cases where the recording medium is filled up during a trip. In addition, the recording medium cannot be stored as is, with data recorded therein, nor can it be given away to a person.
Hence, there is a demand for the realization of a small recording medium which is large in recording capacity and low in cost so that the data photographed by a digital camera can be stored as is, or given away to a person. In PCs, there is also a demand for the realization of an inexpensive small large-capacity recording medium that can be handed to a person.
To meet the aforementioned demands, it is contemplated that the above-described small recording medium may comprise a card disk drive which is loaded in electronic equipment such as a PC and a digital camera, and a magnetic disk cartridge which is loaded in the small card disk drive. That is, it is contemplated that such a magnetic disk cartridge may comprise a housing with a shutter, and a flexible magnetic disk, rotatably supported within the housing, which is capable of high-density recording and has a recording capacity of 200 MB or larger. Examples of magnetic recording media with a high recording density are a recording medium with a thin metal film formed by vapor deposition or sputtering, and a recording medium employing barium ferrite powder or ferromagnetic magnetic powder. An example of a magnetic recording medium with a high recording density employing barium ferrite powder is disclosed in U.S. application Ser. No. 10/266,584.
The “magnetic recording medium with a high recording density employing barium ferrite powder” is a magnetic disk containing barium ferrite powder in a magnetic layer, and is formed from a material that is capable of a high recording density. The magnetic disk may be constructed of a magnetic recording medium. The disclosed magnetic recording medium has a non-magnetic substrate, a non-magnetic layer which includes both non-magnetic powder and a binder, and a magnetic layer which includes both ferromagnetic powder (which is hexagonal-system ferrite powder) and a binder. The non-magnetic layer and the magnetic layer are formed on at least one surface of the non-magnetic substrate in the recited order. In the non-magnetic layer, the quantity of carbon black whose average particle diameter is 10 to 30 nm is 10 to 50 weight parts with respect to 100 weight parts of the aforementioned non-magnetic powder. The thickness of the magnetic layer is 0.2 μm or less. According to an electron-beam microanalysis, the standard deviation (b) of the strength of an element with respect to an average strength (a) which results from ferromagnetic powder is 0.03≦b/a≦0.4. The center plane average roughness Ra of the magnetic layer is 5 nm or less, and the 10-point average roughness Rz is 40 nm or less. In a magnetic disk employing the above-described magnetic recording material, information is recorded or reproduced by employing a magnetic head, such as an MR head, which is capable of a high recording density.
The above-described magnetic recording medium can realize a high recording density of 200 MB or larger, preferably 500 MB or larger. Therefore, if a still image has about 1 MB of data per image, the magnetic recording medium can store 500 images. In the case of a motion picture, the magnetic recording medium can store image contents of about 30 minutes. Thus, the magnetic recording medium can store a motion picture photographed by a digital camera, or a motion picture transmitted by a portable telephone. As a result, users can conveniently use the magnetic recording medium. Furthermore, the magnetic recording medium can be conveniently used in PCs as an inexpensive large-capacity data storage medium. Thus, the convenience of the magnetic recording medium is great.
Note that card disk drives are loaded in electronic equipment such as a PC, a digital camera, etc. In the case of a PC shown in FIG. 6A, a card disk drive 6 is connected electrically with the socket 4 of the receiving portion of a card 2 that is inserted in the card slot of the PC. In the case of a digital camera 3 shown in FIG. 6B, a card disk drive 6 is connected electrically with the socket of the receiving portion 5 of the camera 3.
Therefore, the card disk drive 6 shown in FIG. 6A or 6B is extremely small in size and has, for example, a length of 38 to 55 mm, a width of 35 to 51 mm, and a thickness of 3 to 5 mm. A disk cartridge 8 that is loaded in the card disk drive 6 has, for example, a length and a width of 25 to 36 mm and a thickness of 1 to 3 mm.
To put the aforementioned magnetic recording medium to practical use, the recording capacity is required to be as large as possible, as previously described. The central portion of a conventional magnetic recording medium is mounted on a disk-mounting hub, which is spun by a spindle provided in a disk drive. Since a portion of the magnetic recording medium that is occupied by the hub cannot be used, an area that can be used for recording is narrowed by the amount corresponding to the hub. As the size of a magnetic recording medium becomes smaller, an area that cannot be used by the hub will have a greater effect on the recording capacity. Note that a magnetic disk is mounted on the hubby employing a hot melt, adhesive agent, etc. Therefore, in the case where a magnetic disk is small, great deformation occurs in the disk when the magnetic disk is mounted on the hub. Because of this, surface runout occurs during rotation of the disk, and consequently, there is a possibility that the magnetic disk cannot be used. Particularly, great deformation tends to occur in a portion of the recording surface near the hub. Thus, in the vicinity of the hub, a recording area that can be used is restricted.